Dental impression trays are used for receiving a curable composition to obtain an impression of the dentition or part thereof. When plaster or another material is poured into said mould, a model of the dentition or part thereof can be obtained to serve as a working basis for the dental technician.
DE 26 19 799 C2, now issued in a related case as U.S. Pat. No. 4,085,507 to Lehn et al., discloses another dental impression tray which is similar to the one referred to above. It has inner and outer wall members provided with beaded terminal edges to exert a retentive force on the impression material.
DE 26 16 799 C2 discloses another dental impression tray which is largely similar to the one referred to above. It has inner and outer wall members provided with beaded terminal edges to exert a retentive force on the impression material.
Particularly with the use of silicones as the impression material, so-called flow streaks appear in the hardened material in the transitional area between tooth or stub and gingiva, i.e. voids which have not been filled out by the material flowing during the moulding process. Such voids are produced on account of the flow properties of the material when the tray filled with the impression material is fitted to the jaw, and these voids are additionally promoted by the hydrophobic property of the silicones. The material which is displaced by the teeth and the gingiva will flow in accordance with physical laws of flow past individual small undercuts intermediate the tooth and the gingiva, while the above-mentioned small voids may form similar to the burbling phenomenon on an airfoil.
These voids will corrupt the impression so that the subsequent work by the dental technician on such sites, which are important for fitting, will be made with insufficient precision thereby increasing the labour of the dental technician and/or the dentist, or in more severe cases the entire mould will become useless.
It is an object of the present invention to provide a dental impression tray with which precise impression may be taken. A more specific object of the invention may be seen in preventing the formation of the mentioned voids in the impression material.
To meet this object, the dental impression tray of the present invention has a wall member provided on an inner surface of the tray, the wall member, in the working position of the tray, facing the patient""s jaw and being disposed at least partly opposite that side of the dental arch which faces the patient""s palate or tongue, wherein the wall member has a surface with, at a terminal edge, extends towards a transition region between the patient""s dental arch and gingiva.
When the tray is pressed against the jaw, this surface will cause the flow of the impression material to be directed into the transition area between the dental arch and the gingiva so that it cannot easily flow past narrow cavities or undercuts existing in said area but will rather fill out such formations. In this way the mentioned voids in the impression material can be eliminated or at least reduced, resulting in a better fit of the finished dental replacement part.
At the same time, the wall member results in a saving of moulding material.
In an embodiment, the surface of the wall member is concavely curved to permit the flow of the impression material to be directed in an even more controlled way to those sites which up to now could be filled only with difficulty.
Preferably, the terminal edge of the wall member, in the working position of the tray, cooperates with the patient""s dental arch to form a region of reduced cross-section of flow. This leads to increased pressure in that portion where there is a tendency towards void formation.
The wall member may configured as a curved web which, in the working position of the tray, extends substantially along the entire dental arch so that the invention is effective throughout the dental arch.
Alternatively, the wall member is provided with the concavely curved surface along only part of its length, which makes the tray easier to manufacture.
In another preferred embodiment, the tray has an outer peripheral wall defining an outer top edge of the tray, and the wall member forms an inner top edge which is situated substantially above the outer top edge. In this configuration, the dental arch is prevented from being forced right through onto the bottom of the tray.